1. Field of the Invention
The present invention relates to data processing, and more particularly, to processing for preventing manipulation of markup data.
2. Description of the Related Art
Markup data in which the attribute of each element is defined using a markup language has been used as data of a document or the like dealt with in a computer. An SGML (Standard Generalized Markup Language), an HTML (Hyper Text Markup Language) or the like is used as such a markup language.
Recently, various data formats using an XML (Extensible Markup Language), serving as such a markup language, have been proposed.
The XML represents a data item using a tag including “<” and “>”, in a readable data format described by text data, such as “<Tag>” or “</Tag>”, and can represent various data by surrounding another data by such tags so as to provide a nest structure. When data is not included within a data item represented by a tag, a description, such as “<Tag/>”, may be provided. It is also possible to describe characteristic data relating to a tag, which is called a property, within the tag. Such an approach is realized, for example, by interpolating a character string in the form of “property name=“value”” in the tag by separating the character string from the tag name (“Tag” in this example) with a blank character, such as “<Tag prop=“Property”> . . . </Tag>”.
The XML also has a data block called DTD (Document Type Definition), in order to specify the structure of the tag in succeeding actual XML data (Body).
The XML also can add information when rendering the data using style sheets, such as an XSL (Extensible Style Language) or CSS (Cascading Style Sheets), and define a hyperlink between data by using XLink or XPointer.
There is an SMIL (Synchronized Multimedia Integration Language), an SVG or the like as an example of the data format using the XML.
As described above, since the XML is a data format including text data, it can be easily formed or edited using ordinary document editing software (a text editor or the like). This is advantageous from the viewpoint of easing handling of the XML.
However, for example, even if data not to be manipulated, such as information relating to the copyright (the author's name, the registration number of the copyright, or the like) is partly included in the data, the portion of the copyright data can be easily changed, i.e., easily manipulated by a third party.
In order to prevent the manipulation of the data, an approach can, for example, be considered in which the entire data is encoded using a secret key of a public-key cryptographic system). In such an approach, however, in order to read encoded data, it is necessary to provide software and a public key corresponding to the public-key cryptographic system, and the data becomes entirely meaningless for a person who does not have such items. When merely reading data without confirming information relating to the copyright, it is desirable to be able to easily refer to the contents of the data without such limitation.
It is also desirable that the procedure is simple for a person who confirms information relating to the copyright.